Due to actualization of environmental problems in recent years, hybrid cars and electric vehicles have spread. Then, as an air conditioner which is applicable to such a vehicle, there has been developed an air conditioner including a compressor to compress and discharge a refrigerant, a radiator disposed on a vehicle interior side to let the refrigerant radiate heat, a heat absorber disposed on the vehicle interior side to let the refrigerant absorb heat, and an outdoor heat exchanger disposed outside the vehicle interior to let the refrigerant radiate heat or absorb heat, and there are changed and executed respective operation modes of a heating mode to let the refrigerant discharged from the compressor radiate heat in the radiator and let the refrigerant from which the heat has been radiated in this radiator absorb heat in the outdoor heat exchanger, a dehumidifying and heating mode to let the refrigerant discharged from the compressor radiate heat in the radiator and let the refrigerant from which the heat has been radiated in the radiator absorb heat in the heat absorber and the outdoor heat exchanger, an internal cycle mode to let the refrigerant discharged from the compressor radiate heat in the radiator, decompress the refrigerant from which the heat has been radiated, and let the refrigerant absorb heat in the heat absorber, a dehumidifying and cooling mode to let the refrigerant discharged from the compressor radiate heat in the radiator and the outdoor heat exchanger, decompress the refrigerant from which the heat has been radiated, and let the refrigerant absorb heat in the heat absorber, and a cooling mode to let the refrigerant discharged from the compressor radiate heat in the outdoor heat exchanger, decompress the refrigerant from which the heat has been radiated, and let the refrigerant absorb heat in the heat absorber (e.g., see Patent Document 1).